1. Field of the Invention
The present invention relates to a sheet feeding device for feeding sheets, a sheet post-processing system, and an image formation system including the sheet feeding device.
2. Description of the Related Art
Conventionally, there have been image formation systems which control the insertion of sheets such as book covers, inside covers, back covers following bookbinding, and so forth, at such a timing that the sheets can be inserted in a predetermined output sequence without passing through an image formation apparatus and fixing means, in order to not deteriorate quality of printing images. Such an image formation system has been disclosed in Japanese Patent Laid-Open No. 2000-211803. The image formation system described in the aforementioned Japanese Patent Laid-Open comprises a multiple inserter 900 at an upper portion of a sheet post-processing device 500 connected to an image formation apparatus 10 as shown in FIG. 8, which can insert inserting sheets loaded in a tray 901 of the multiple inserter 900 at a timing which enables the sheets to be inserted in a predetermined output sequence. A bundle of sheets to be set are loaded into the tray 901 with the front side thereof facing up in order to prevent a mix-up between the front and back sides of inserting sheets caused by setting errors by the operator. The bundled sheets which form book covers and combining sheets loaded in the tray 901 are sequentially separated and transported to a transport path according to the post-processing mode of the sheet post-processing device 500 set from an unshown operating unit. In the event that the sort mode or the staple sort mode is set as a post-processing mode, the sheets need to be transported to a processing path 552 and sort path 554 with the front side thereof facing down. Accordingly, the inserting sheets in the tray 901 are transported from an inserter path 908 to the processing path 552 and sort path 554. On the other hand, in the event that the bookbinding mode is set as a post-processing mode, the sheets need to be transported to a bookbinding path 553 with the front side thereof facing the left side. Accordingly, the inserting sheets in the tray 901 are transported from the inserter path 908 to the processing path 552 and sort path 554, and temporally stopped there, and transported to the bookbinding path 553 in the reverse direction.
However, when the device is able to determine whether the inserting sheets are set faced up in the inserter tray 901 thereby preventing mix-ups between front and back sides of the inserting sheets due to setting errors by the operator, reversing operations of the inserting sheets need to be performed by either the sort mode, the staple sort mode, or the bookbinding mode set from the operating unit, resulting in marked reduction in productivity of the image formation system.
On the other hand, in the event the device is one in which the side of the inserting sheets to face up in the inserter tray 901 according to the selected post-processing mode is selectable, setting errors by the operator are brought about, resulting in mismatching of the sides of the inserting sheets.